Family trying to run my life grrrrr

I am only 19 but I have two loving stepdaughters who both have kids of there own. I love watching my granddaughters but my family keeps telling me I need to start thinking straight and tell the girls I can't watch kids that are not mine. I try to explain to them that I don't see them as step kids that to me they are my girls and those are my grandbabys. They are starting to make rude coments when the girls are over how do I tell them to stop trying to make my girls hate me

I have tried to tell them that and they just tell me no they are not and it doesnt help that we live with them right now because our house burned down and yes I get that a lot that a 19 yr old with grand kids but I wouldn't trade them for the world